Polyurethane foam insulation is an integral component in residential and commercial building insulation systems and virtually all refrigerators and freezers produced today. Thermal insulating performance is particularly uncompromisable in the light of recent federally mandated reductions in applicance energy consumption. As the industry strives for greater energy efficiency it is now faced with a second environmentally driven issue, that being, the attack of fully halogenated chlorofluorocarbons on the earth's protective ozone layer. International agreement to eventually ban these materials means that the use of certain chlorofluorocarbons such as CFC-11, as a common blowing agent for foamed polyurethane and polyisocyanurate foams, must come to an end. As a key step toward that goal, utilization of carbon dioxide from the water-isocyanate reaction in the foaming formulation as a co-blowing agent will likely play an important role in most rigid polyurethane and polyisocyanurate foam applications in the near future.
The most likely approach to using less chlorofluorocarbons is the use of increased amounts of water in the water-isocyanate reaction to produce carbon dioxide as the blowing agent rather than using chlorofluorocarbons.
However, a number of problems are inherent in the use of high levels of water in foamable systems. Most serious is that certain gases trapped in the cured foam cells decrease the insulating performance of foams. As the chlorofluorocarbons are replaced with carbon dioxide this insulating capacity decreases. Carbon dioxide is a much better conductor of heat energy compared to chlorofluorocarbons. Reduced foam flow during processing will also be observed due to the increased resin viscosity obtained with lower levels of chlorofluorocarbons which tend to act as interim solvents in the foaming formulation. The higher resin viscosity will also result in less efficient component mixing. This will in turn result in processing difficulties and coarser-celled foams. Higher levels of water in the foam formulation also leads to more friable foams which exhibit poor adhesion to the applicance cabinet and to facer materials used in laminated foams, a requirement in the use of the foams in refrigerators and freezers and commercial and residential construction applications. Finally, the proclivity of the carbon dioxide to quickly diffuse out of the polyurethane foam formulation puts greater demands on the structural integrity of the foaming polymer. This will often lead to foam shrinkage as the internal cell pressure in the foam drops due to carbon dioxide effusion from the foaming mixture.
The invention disclosed herein seeks to overcome some of the problems in the prior systems for obtaining polyurethane and polyisocyanurate foams having enhanced benefits.
Thus it is an object of this invention to provide system flowability of the reacting foam mixture.
It is a further object of this invention to provided a foam with an insulating capability equal to the foams that are provided by the chlorofluorocarbon blown systems.
Yet another object of this invention is to provide foams having the requisite density for use in insulating applications. and finally, it is an object of this invention to provide a method of preparing polyurethane and polyisocyanurate foams which are easily demolded.